This is a revised Program Project Grant, the central theme is that endocrine, paracrine and autoerine factors produced by the epithelial, vascular smooth muscle, endothelial and interstitial cells play an important role in regulating salt and water excretion by the kidney, and thus blood pressure, by altering renal hempdynamics, changing NaCI reabsorption and mediating cross-talk between cells. The central hypothesis to be tested is that blood pressure regulation by the kidney occurs via integration of the actions of prch and anti-hypertensive agents on nephron transport, renal vascular resistance, release of renal hormones and cross-talk between epithelial and vascular cells. Defects in the integration process and/or actions of pro- and anti-hypertensive agents lead to renal dysfunction, salt retention and hypertension. This hypothesis will be tested in four projects that break new ground in our understanding of how the kidney regulates blood pressure. Project 1 will study whether increasing luminal flow in the thick ascending limb stimulates nitric oxide (NO) production by NO synthase 3, the signaling cascades involved, the effects of flow-induced NO on NaCI reabsorption, and whether a defective response to flow-stimulated NO production enhances sait retention and promotes salt-sensitive hypertension. Project 2 will test whether NO inhibits thick ascending limb NaCI reabsorption by activating cGMP-stimulated phosphodiesterase 2 (PDE2), reducing cAMP, and thus decreasing Na/K/2CI cotransport. It will also test in Dahl salt-sensitive rats whether a reduction in NOinduced inhibition of NaCI reabsorption and hypertension is caused by diminished PDE2 activity and enhanced cGMP degradation by phosphodiesterase 5. Project 3 will test whether heme oxygenases in the macula densa produce carbon monoxide (CO) and biliverdin, which act synergistically and in an autocrine manner to inhibit tubuloglomeailar feedback. It will also test whether CO acts by stimulating cGMP which inhibits Na/K/2CI cotransport, and blocks ATP release and biliverdin acts by decreasing superoxide, thereby increasing NO. Project 4 will test whether increased extracellular Ca inhibits renin release by activating Ca sensing receptors on juxtaglomerular cells which increases intracellular Ca and reduces cAMP production by inhibiting adenylyl cyclase-V and stimulating phosphodiesterase 1. These studies will be performed in vitro at the subcellular, cellular, and isolated tissue levels and in vivo using both acute and chronic models, and genetically manipulated mice. The four projects will be supported by three core units (Administrative, Molecular Biology and Analytical, and Imaging) that will facilitate the scientific effort. The Program Project Grant will provide integration of our efforts, continued collaboration and shared ideas and expertise. Thus it will accelerate acquisition of knowledge of the novel mechanisms by which the kidney regulates blood pressure, and may provide new targets for anti-hypertensive drugs.